那些年啊，那些事---V4L2采集图片源码分享

把v4l2采集图片测试程序，贴在这和大家共享，在此基础上可以使实现视频的采集，只不过在pc机上写个上位机进行显示或者直接写个Qt在开发板上显示即可，

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采集效果如下：

源码如下：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>

#include <getopt.h>

#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
#include <malloc.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/time.h>
#include <sys/mman.h>
#include <sys/ioctl.h>

#include <asm/types.h>
#include <linux/videodev2.h>

#define CLEAR(x) memset (&(x), 0, sizeof (x))

struct buffer {
void * start;
size_t length;
};

static char * dev_name = "/dev/video0";
static int fd = -1;
struct buffer * buffers = NULL;

FILE *file_fd;
static unsigned long file_length;
static unsigned char *file_name;

int main (int argc,char ** argv)
{
struct v4l2_capability cap;
struct v4l2_format fmt;

file_fd = fopen("test.jpg", "w");

fd = open (dev_name, O_RDWR /* required */ | O_NONBLOCK, 0);

ioctl (fd, VIDIOC_QUERYCAP, &cap);

CLEAR (fmt);
fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
fmt.fmt.pix.width = 640;
fmt.fmt.pix.height = 480;
fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV;
fmt.fmt.pix.field = V4L2_FIELD_INTERLACED;
ioctl (fd, VIDIOC_S_FMT, &fmt);

file_length = fmt.fmt.pix.bytesperline * fmt.fmt.pix.height;

buffers = calloc (1, sizeof (*buffers));

buffers[0].length = file_length;
buffers[0].start = malloc (file_length);

for (;;)
{
fd_set fds;
struct timeval tv;
int r;

FD_ZERO (&fds);
FD_SET (fd, &fds);

/* Timeout. */
tv.tv_sec = 3;
tv.tv_usec = 0;

r = select (fd + 1, &fds, NULL, NULL, &tv);

if (-1 == r) {
if (EINTR == errno)
continue;
printf ("select");
}

if (0 == r) {
fprintf (stderr, "select timeout\n");
exit (EXIT_FAILURE);
}

if (read (fd, buffers[0].start, buffers[0].length))
break;
}

fwrite(buffers[0].start, buffers[0].length, 1, file_fd);

free (buffers[0].start);
close (fd);
fclose (file_fd);
exit (EXIT_SUCCESS);
return 0;
}